The present invention relates to a high DC voltage generator which is particularly useful in television receivers for generating a high DC voltage that drives the intensifier electrode of the cathode ray tube.
The cathode ray tube of a television receiver requires a high DC voltage for its intensifier electrode and this high voltage is derived from a flyback circuit that utilizes the horizontal sweep current of the receiver. The flyback circuit includes a flyback transformer of which the primary winding is connected to the horizontal sweep generator and the secondary winding is connected to a voltage multiplier. In response to a rapid change in sweep current, a high voltage flyback pulse is induced in the secondary winding and multiplied in amplitude and stored on capacitors of the voltage multiplier to generate a high DC output voltage.
To meet the increasing demands for high quality color television receivers, it is necessary to minimize the amount of ringing current of the flyback circuit which is generated by the resonance of a current in the secondary winding to the frequency determined by the leakage inductance and distributed capacitance of the flyback transformer. It is desirable that the resonance occurs at the frequency of one of the ninth, thirteenth and seventeenth harmonics of the flyback pulse, or horizontal sweep current to minimize the ringing current. Another undesirable factor is the voltage output variation which increases with the ringing current.
Other demands for the flyback circuit include requirements for higher voltage output and low cost, compact design. While the high voltage requirement may be met by increasing the number of turns of the transformer's secondary winding, this is accompanied by an increase in the leakage inductance and distributed capacitance and hence a decrease in the ringing frequency. This makes it impossible to meet the requirement that the ringing current be tuned to one of the ninth, thirteenth and seventeenth harmonics of the flyback pulse and contradicts with the requirement for low cost, compact design.